Upcoming C-17 tests will be a stepping stone toward improving national energy security as well as toward prompting interest in commercial industry.

by Roger DrinnonScott AFB IL (AFNS) Sep 12, 2007
Air Mobility Command's chief scientist is now turning his attention to tests to certify Air Force C-17 Globemaster III aircraft to use an alternative fuel mix, which was certified for B-52 Stratofortess Aug. 8. "The C-17 tests will be important because it's a newer aircraft with newer materials and systems," Dr. Don Erbschloe said. "Our goal is to have a standard protocol -- a methodology to establish a military standard for the fuel. (The C-17 tests) will validate the methodology we'll use to certify other aircraft."

By 2010, the Air Force goal is to certify all its aircraft to use the fuel blend which mixes JP-8 with fuel produced using the Fischer-Tropsch process -- a process used to convert carbon-based materials into synthetic fuel.

German chemists Franz Fischer and Hans Tropsch developed the method at the Kaiser Wilhem Institute during the 1920s.

"Essentially, using a number of chemicals and catalysts, what (chemists Fischer and Tropsch) were able to do was to reproduce in a laboratory what it takes the earth millions of years to do with organic matter," Mr. Erbschloe said.

Fischer-Tropsch fuel can be synthesized from any carbon-based material, he said.

"The process starts with carbon-based 'feedstock' -- this could be coal, natural gas or any other carbon-based material. Ultimately, it could be bio-mass or even trash," Mr. Erbschloe said. "The first step is to produce 'synthesis gas' or 'syngas' -- a mixture of carbon monoxide and hydrogen. During the catalysis of syngas, you're building up hydrocarbons, and you get a complex 'organic soup' very much like petroleum."

A Fischer-Tropsch fuel mix has the potential to burn cleaner than JP-8, he said.

"During the process of creating the organic soup, you don't introduce a lot of particulates and unwanted materials like sulfur compounds," Mr. Erbschloe said. "Indications are that (Fischer-Tropsch fuel) doesn't leave sooty trails."

"In (the B-52 engine) tests, the use of the alternative fuel blend was found to reduce soot emissions by 30 percent at max power and by 60 percent at idle," said Dr. Tim Edwards, a senior chemical engineer for the Air Force Research Laboratory's Fuels Branch. "Sulfur emissions were reduced by 50 percent. These emissions reductions are due to the very high quality of the Fischer-Tropsch fuel blend component."

Although the Fischer-Tropsch process generates excess carbon dioxide, Mr. Erbschloe said he remains confident technologies will emerge soon to capture and store the carbon dioxide generated by the process.

Until more research is done, Fischer-Tropsch fuel is mixed with JP-8 to ensure the fuel contains adequate "aromatics" -- elements found in traditionally-produced fuels and lacking in Fischer-Tropsch fuel, he said.

"Aromatics might be a factor in preventing fuel leaks," Mr. Erbschloe said. "It turns out aromatics might help various seals and o-rings expand and seal properly in aircraft engines during operation."

As fuel prices rise, synthetic fuel becomes economically viable with the potential to reduce dependency on foreign energy sources, said Mr. Erbschloe, a former deputy chief operating officer for the Department of Energy's Office of Science.

"The goal is to make the cost of synthetic fuel comparable to buying JP-8," he said.

Upcoming C-17 tests will be a stepping stone toward improving national energy security as well as toward prompting interest in commercial industry. He said commercial aviation already is working with the Air Force to certify more aircraft to use the fuel blend. The former Air Force command pilot with 3,900 flying hours said Air Force standardization efforts will help define the certification process.

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